1. Field of the Invention
The present invention relates to a plasma treating apparatus and a plasma treating method for applying a predetermined treatment on a substrate surface by using plasma generated in a dielectric container.
2. Description of the Related Art
Various types of plasma treatments, for example, plasma etching and chemical vapor phase deposition (CVD), are known for treating substrates. Apparatuses using plasma generated in a dielectric container have also been used for substrate treatment. In recent years, apparatuses using helicon wave excited plasma have been intensively used as apparatuses which are able to form low-pressure high-density plasma, among such apparatuses forming plasma in the dielectric container.
FIG. 4 is a cross-sectional view illustrating an outline of a plasma treating apparatus using helicon wave excited plasma as an embodiment of a conventional plasma treating apparatus. The apparatus shown in FIG. 4 has a vacuum chamber 1 with a pumping system 11, a substrate holder 2 for holding a substrate 20 at a predetermined position in the vacuum chamber 1, and a dielectric container 3 in which plasma used for the treatment of the substrate 20 is generated.
The vacuum chamber 1 has an opening at the top wall facing the substrate 20 on the substrate holder 2. The dielectric container 3 is a cylindrical member of which one end is an opening and the other end is formed to a semi-spherical shape. The dielectric container 3 is provided on the top wall of the vacuum chamber 1 so as to mount the periphery of the opening of the dielectric container 3 onto the periphery of the opening of the top wall of the vacuum chamber 1.
A helical antenna 41 is provided at the circumference of the dielectric container 3 for applying high frequency electric power inside the dielectric container 3. The antenna 41 connects with a high frequency power source 43 through a matching device 42 so that a predetermined high frequency electric power is guided into the dielectric container through the antenna 41. A magnetic field generating means 5 comprising an electromagnet is provided at the circumference of the antenna 41. The magnetic field generating means 5 generates a magnetic field in the dielectric container to generate helicon wave excited plasma. The vacuum chamber 1 also has a gas inlet system 6 to introduce a gas for generating plasma.
In the conventional plasma treating apparatus as shown in FIG. 4, a gas is introduced into the vacuum chamber 1 from the gas inlet system, and high frequency electric power is guided into the dielectric container from the antenna 41. A helical induction field is generated in the dielectric container 3 by means of the helical antenna 41. Thus, the helicon wave excited plasma is generated, and the substrate 20 is subjected to a plasma treatment.
For example, plasma etching is carried out by generating the above-mentioned plasma while introducing an etching gas, or by adding an etching gas into a plasma-generating gas.
The helicon wave excited plasma is a low-pressure high-density plasma generated according to a principle that electromagnetic waves having a frequency lower than that of plasma propagate in the plasma without decay when a strong magnetic field is applied.
In such a plasma treating apparatus, an organic thin film may deposit on the inside surface of the dielectric container. In a plasma etching apparatus, for example, a resist film comprising organic materials is deposited on the surface of the substrate. Although the resist film is resistant to plasma, the film partly evaporates when the film is exposed to high-temperature, high-density plasma. A part of the evaporated resist film adheres to the inside surface of the dielectric container after floating in the space in the dielectric container. The organic thin film deposits on the inside surface of the dielectric container due to the proceeded adhesion of the evaporated resist film.
When the deposited film grows to a certain thickness, the thin film will peel away from the inside surface of the dielectric container and fall upon the substrate which is provided just under the dielectric container, as shown in FIG. 4. The fallen thin film on the substrate causes defects of the semiconductor circuit formed on the substrate, such as a disconnection or shortening of the circuit. Further, when a conductive organic thin film deposits on the inside surface of the dielectric container, the high frequency electric power may be extraordinarily guided into the dielectric container. Moreover, when plasma emission photospectrometry through the dielectric container is carried out, the deposited film may shade light emitted by plasma, resulting in unsuccessful photospectrometry.
A thin film of material other than the material for the resist film is also deposited on the inside surface of the dielectric container. For example, in recent dry etching, an organic gas, such as C.sub.3 F.sub.8, C.sub.4 F.sub.8 or CH.sub.2 F.sub.2, is used to improve the selectivity to the substrate material. It is known that such organic gas partly decomposes due to plasma, adheres to the inside surface of the dielectric container, and finally deposits an organic thin film. Etching of an organic thin layer formed on the substrate surface and thin film deposition by CVD using an organic gas may also deposit an organic thin film on the inside surface of the dielectric container.
Periodic cleaning is carried out to remove the deposited film, so that the above-mentioned problem does not occur. However, such cleaning process requires suspending plasma treatment. Heavy deposition will require much time for cleaning and decrease the productivity of the apparatus. To suppress the deposition of the organic thin film, heating the dielectric container with a heating wire during the treatment is proposed, as described in Japanese Patent Laid-Open Nos. 58-53833 and 5-94971, and Japanese utility model Laid-open No. 2-38470.
In the method for suppressing the deposition of the thin film described in Japanese Patent Laid-Open No. 58-53833, when the high frequency electrode of the antenna is provided at the circumference of the dielectric container like the device generating helicon wave excited plasma, the high frequency electric power radiated from the antenna may not effectively couple with plasma due to the heater provided near the dielectric container. Any means for not interrupting the propagation of the high frequency electric power, for example, a compact heater, or a plurality of divided heaters, may be used in order to solve the problem. However, it is hard to uniformly heat the dielectric container by such means. Further, since the antenna must be thermally insulated so as not to be heated excessively, the structure of such an apparatus would be complicated.
In the above-mentioned Japanese Patent Laid-Open No. 5-94971, the deposition can be suppressed by heating the dielectric container with warm water to 80.degree. C. However, it is substantially difficult to suppress the deposition of the organic thin film on the dielectric container by heating to a temperature around 80.degree. C. This method has another drawback in that a larger area is needed to provide the apparatus with a system for supplying and circulating warm water. When the dielectric container integrated with a water-circulating pipe is made of quartz, warm water may leak into the vacuum chamber through cracks caused due to unexpected damage of the dielectric container, resulting in much labor and time for cleaning the vacuum chamber.
Heating the plasma-generating container has been used with microwave powered etching devices, as shown in Japanese Utility Model Laid-Open 2-38470.
Regardless of whether a single wafer processing apparatus or a batch apparatus is employed, the same or different kinds of plasma treatments are repeated in one plasma deposition apparatus. After completion of one plasma treatment, gases used and formed during the treatment still remain in the vacuum chamber. Heating processes disclosed in the above-mentioned patents and utility model do not include heating of the dielectric container during the time period in which the plasma treatment is halted. The dielectric container will be cooled by outgoing radiation after the treatment. As a result, the thin film will easily deposit on the inside surface of the dielectric container due to the remaining gases.
Although such a problem may be reduced more or less by evacuating the vacuum chamber after the treatment, perfect removal of the remaining gases requires a long period of time, resulting in an unsatisfactory decrease in productivity.